Coated abrasive articles are conventionally made by electrostatic coating (e-coat) the abrasive particles onto a make layer precursor (also known in the art as a “make coat”) on a backing or drop coating the abrasive particles (also referred to in the art as abrasive grains) onto the make layer precursor, which is then cured to form a make layer resulting in a make layer (also termed a “make coat” in the art). A size layer precursor is disposed on the make layer and abrasive particles, and the size layer precursor is cured, and a size layer (also termed a “size coat” in the art). Optionally, but commonly, a supersize layer (which may contain, grinding aids, lubricants, etc.) is disposed on the size layer. The make and size layers generally include a thermosetting resin (e.g., phenolic resin, aminoplast resin, curable acrylic resin, cyanate resin, and combinations thereof).
Controlling the z-direction rotational orientation of the abrasive particles in a coated abrasive article is not possible using conventional electrostatic deposition methods to propel the abrasive particle vertically against the force of gravity onto a make layer by use of an electrostatic field thereby erectly applying the abrasive particles as shown in U.S. Pat. No. 2,370,636 (Carlton). The abrasive particles in the coated abrasive article generally have a random z-direction rotational orientation since the particle's rotation as it is being removed from the conveyor belt by the electrostatic field is random and uncontrolled. Similarly, in drop-coated abrasive articles, the particle's z-direction rotational orientation is random as the particles are fed from the hopper and fall by the force of gravity onto the make layer precursor.
Triangular shaped abrasive particles and abrasive articles using the triangular shaped abrasive particles are disclosed in U.S. Pat. No. 5,201,916 (Berg), U.S. Pat. No. 5,366,523 (Rowenhorst); and U.S. Pat. No. 5,984,988 (Berg). In one embodiment, the abrasive particles' shape was an equilateral triangle. Triangular shaped abrasive particles are useful in manufacturing abrasive articles having enhanced cut rates.
PCT International Publ. No. WO 2012/112305 A2 (Keipert) discloses coated abrasive articles manufactured through use of precision screens having precisely spaced and aligned non-circular apertures to hold individual abrasive particles in fixed positions that can be used to rotationally align a surface feature of the abrasive particles in a specific z-direction rotational orientation. In that method, a screen or perforated plate is laminated to an adhesive film and loaded with abrasive particles. The orientation of the abrasive particles could be controlled by the screen geometry and the restricted ability of the abrasive particles to contact and adhere to the adhesive through the screen openings. Removal of the adhesive layer from the filled screen transferred the oriented abrasive particles in an inverted fashion to an abrasive backing. The method relies on the presence of adhesive which may be cumbersome, prone to detackifying (e.g., due to dust deposits) over time, and which may transfer to the resultant coated abrasive article creating the possibility of adhesive transfer to, and contamination of, a workpiece.
U.S. Pat. Appln. Publ. 2013/0344786 A1 (Keipert) discloses a coated abrasive article having a plurality of formed ceramic abrasive particles, each having a surface feature. The plurality of formed ceramic abrasive particles is attached to a flexible backing by a make coat comprising a resinous adhesive forming an abrasive layer. The surface feature having a specified z-direction rotational orientation, and the specified z-direction rotational orientation occurs more frequently in the abrasive layer than would occur by a random z-direction rotational orientation of the surface feature. The term “formed abrasive particle” as used therein excludes randomly sized abrasive particles obtained by a mechanical crushing operation.